[ntp:questions] GPS/PPS and "enable calibrate"

David Lord snews at lordynet.org
Fri Sep 6 07:07:28 UTC 2013


Horvath Bob-BHORVAT1 wrote:
> 
> -----Original Message-----
> From: questions-bounces+bob.horvath=motorolasolutions.com at lists.ntp.org [mailto:questions-bounces+bob.horvath=motorolasolutions.com at lists.ntp.org] On Behalf Of WOLfgang Schricker
> Sent: Thursday, September 05, 2013 1:08 PM
> To: questions at lists.ntp.org
> Subject: Re: GPS/PPS and "enable calibrate"
> 
> Horvath Bob-BHORVAT1 schrieb:
>> I am trying to get a raspberry pi GPS-based stratum server functioning and I am confused how to use the "enable calibrate" function.  
> [...]
>> The server is a raspberry pi with the Adafruit MTK339 GPS chipset.  It is running the image from here... http://ntpi.openchaos.org/downloads/
>>
>> BTW, thanks to all the raspberry pi NTP guys out there that have gotten me this far!!
>>
>> Bob
>>
> Hi,
> this runs perfectly for me:
> <http://open.konspyre.org/blog/2012/10/18/raspberry-pi-time-server/>.
> 
> OK, maybe I'll have to try that image.  
> 
> In general though, when it comes to this line...
> 
>   fudge 127.127.20.0 flag1 1 time2 0.496
> 
> ... how do you know what value to set for time2?  
> 
> Did you got through the instructions here?
> 
> http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html
> 
> ... or are you using 0.496 - what is shown on the http://open.konspyre.org/blog/2012/10/18/raspberry-pi-time-server/ ?
> 

I couldn't find a generic method on that page.

I have used both Garmin 18x-LVC and a Sure development board
and setup both using peer_summary over several days to get a
reasonable value for the time2 offset. That value is tied to
both the make/model and firmware version of the GPS. My Garmin
would wander more than +/- 50 ms so the time2 value used isn't
that critical but a large 'tos mindist' might be needed.

The method I use is to set a reliable internet source as prefer
and have 127.127.20.0 noselect. After a few days take the mean
value of the peer_summary output.

Last five days of peer_summary for my Sure gps NetBSD-6-i386 via-600MHz

        ident     cnt     mean     rms      max     delay     dist     disp
127.127.20.2    1350    0.136   19.639   88.092    0.000    2.519    1.749
127.127.20.2    1346    1.358   21.361   79.671    0.000  939.133    2.980
127.127.20.2    1350    0.642   20.467   90.241    0.000    2.709    1.757
127.127.20.2    1350    5.020   21.552   70.508    0.000    2.528    1.752
127.127.20.2    1350    3.947   22.530   73.186    0.000    2.309    1.714

127.127.22.2    1350    0.000    0.004    0.032    0.000    0.930    0.930
127.127.22.2    1344    0.003    0.069    2.459    0.000  938.257    2.142
127.127.22.2    1350    0.001    0.004    0.033    0.000    0.934    0.934
127.127.22.2    1350    0.001    0.005    0.033    0.000    0.934    0.934
127.127.22.2    1350    0.001    0.004    0.031    0.000    0.934    0.934






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